In recent years, the distance between a head and a disk has shown a tendency to become smaller because of the necessity to make magnetic disk devices have a higher recording density. The speed of revolution of a disk has also shown a tendency to increase because of the necessity to perform read/write at a high speed. This causes the head and the disk to come into contact more frequently, and moreover come into contact at a higher speed than ever. Hence, it is foreseen that disks will slide as the operating conditions become more severe than ever. Accordingly, in order to prevent magnetic layers from wearing away because of such a sliding movement, lubricants used in the outermost layers of magnetic disks have been improved in variety.
For example, a fluorine-containing compound such as a compound having piperonyl groups at both terminals of a perfluorooxyalkylene chain (Japanese Patent Application Laid-open No. 61-4727) is proposed as a lubricant which may be coated on the surfaces of magnetic disks to improve the lubricity of their surfaces to reasonably restrain the wear of magnetic layers.
However, such a lubricant may be gradually scattered by the sliding of a head. This is considered to be due to the lubricant being physically scraped off by sliding movement or due to volatilization caused by heat energy produced by sliding movement. Accordingly, low-scattering lubricants are desired since the use of a disk for a long time may cause the lubricant layer on the disk surface to become thin or, in some cases, may cause its underlying layer to become laid bare in parts.
In particular, in recent years, as the distance between the head and the disk is made smaller in order to make magnetic disk devices have a higher recording density, the head and the disk come into contact very frequently. Thus, the lubricants must be durable to cope with severe slide conditions. In particular, recently with heads and head sliders being made small-sized, the head tends to have a lower rigidity than ever. Hence, such a head has caused a problem of being broken because of its great stickiness to the disk, when the disk is started to turn.
Accordingly, a first object of the present invention is to provide a fluorine-containing compound having a good sliding performance, low scattering properties and a low stickiness, and a lubricant or surface modifier (water repellent), a lubricating film, a magnetic recording medium and a magnetic recording device which make use of such a compound.
As a lubricant having low scattering properties, Japanese Patent Applications Laid-open No. 8-36741 and No. 8-36742 disclose a proposal of a crown ether compound comprising a perfluorooxyalkyl chain and a crown ether which are linked chiefly by an imino group. Such a compound, however, tends to absorb moisture, therefore tends to cause changes in lubricating performance as a result of moisture absorption, and is not desirable for lubricating films which are used in a highly humid atmosphere over a long period of time.
Accordingly, a second object of the present invention is to provide a fluorine-containing compound having a good sliding performance, low scattering properties and a low moisture absorption, and a lubricant or surface modifier (water repellent), a lubricating film, a magnetic recording medium and a magnetic recording device which make use of such a compound.